U.S. patent number 4,385,134 [Application Number 06/312,686] was granted by the patent office on 1983-05-24 for organotin polysiloxane and acrylic antifouling coating.
This patent grant is currently assigned to Ameron, Inc.. Invention is credited to Raymond E. Foscante, Lee M. Parson, Charles D. Stevens.
United States Patent |
4,385,134 |
Foscante , et al. |
May 24, 1983 |
Organotin polysiloxane and acrylic antifouling coating
Abstract
A marine antifouling coating composition comprises an acrylic
resin such as methyl methacrylate in the range of from 6 to 20% by
weight, a polysiloxane having substituted thereon tributyltin
moieties that are toxic to marine organisms. The polysiloxane is in
the range of from 7 to 25% by weight. The acrylic resin and
polysiloxane are dissolved in a solvent in the range of from 18 to
52% by weight with the balance of the composition in the range of
from 10 to 65% by weight being primarily conventional marine paint
and toxicant agents for augmenting action of the tributyltin
polysiloxane. Copper or copper salts that are effective for
inhibiting growth of marine organisms and facilitating release of
toxins can also be included.
Inventors: |
Foscante; Raymond E. (Yorba
Linda, CA), Stevens; Charles D. (Long Beach, CA), Parson;
Lee M. (Inglewood, CA) |
Assignee: |
Ameron, Inc. (Monterey Park,
CA)
|
Family
ID: |
23212548 |
Appl.
No.: |
06/312,686 |
Filed: |
October 19, 1981 |
Current U.S.
Class: |
523/177; 524/77;
524/500; 525/185; 524/413; 525/342 |
Current CPC
Class: |
C09D
133/06 (20130101); C09D 5/1643 (20130101); C09D
133/06 (20130101); C08L 2666/14 (20130101); C08L
2666/28 (20130101); C08L 83/08 (20130101) |
Current International
Class: |
C09D
133/06 (20060101); C09D 5/16 (20060101); C08L
83/00 (20060101); C08L 83/08 (20060101); A01N
009/00 (); C08G 077/04 (); C09D 005/16 (); C09D
005/38 () |
Field of
Search: |
;260/27R,31.4R,33.6SB,429.7 ;424/184,288 ;525/185,342 ;523/177
;524/77,500,413 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Marquis; Melyn I.
Assistant Examiner: Lilling; Herbert J.
Attorney, Agent or Firm: Christie, Parker & Hale
Claims
What is claimed is:
1. A marine antifouling coating composition comprising:
an acrylic resin selected from the group consisting of methyl
methacrylate, ethyl methacrylate, propyl methacrylate, isobutyl
methacrylate, and n-butyl methacrylate in the range of from 6 to 20
percent by weight;
an organotin polysiloxane having the formula ##STR4## where m is an
average of up to about ten, each X is independently selected from
the group consisting of R and Y; where each R is selected from the
group consisting of hydrogen and alkyl and alkoxyalkyl radicals
containing less than six carbon atoms; where each Y is a
trisubstituted tin radical having the formula ##STR5## where
R.sub.1, R.sub.2, and R.sub.3 are independently selected from the
group consisting of alkyl, cycloalkyl and aryl radicals and
R.sub.1, R.sub.2, and R.sub.3 contain collectively up to 18 carbon
atoms; and the X's are selected so that the ratio of tin atoms to
silicon atoms is in the range of from 0.7:5 to 5:5, the organotin
polysiloxane being in the range of from 7 to 25 percent by
weight;
solvent for the acrylic resin and polysiloxane in the range of from
18 to 52 percent by weight; and
a balance in the range of from 10 to 65 percent by weight of
primarily marine paint and toxicant agents selected from the group
consisting of pigment powders, fillers, thickening agents,
antisettling agents, copper powder, cuprous salts, zinc oxide,
algicides, silica, clay, talc, metal oxides, plasticizers and
slightly water soluble resins.
2. A composition as recited in claim 1 wherein the acrylic resin is
present in the range of from 8 to 12 percent by weight.
3. A composition as recited in claim 2 wherein the organotin
polysiloxane is present in the range of from 12 to 16 percent by
weight.
4. A composition as recited in claim 1 wherein the organotin
polysiloxane is present in the range of from 12 to 16 percent by
weight.
5. A composition as recited in claim 1 wherein the X's are selected
so that the ratio of tin atoms to silicon atoms is in the range of
from 1.3:5 to 2.5:5.
6. A composition as recited in claim 5 wherein the acrylic resin
comprises polymethyl methacrylate in the range of from 8 to 12
percent by weight.
7. A composition as recited in claim 6 wherein the organotin
polysiloxane is present in the range of from 12 to 16 percent by
weight.
8. A composition as recited in claim 5 wherein the organotin
polysiloxane is present in the range of from 12 to 16 percent by
weight.
9. A composition as recited in claim 1 comprising a copper base
antifouling agent selected from the group consisting of copper
powder and cuprous salts in the range of from 10 to 30 percent by
weight.
10. A composition as recited in claim 9 wherein the acrylic resin
is present in the range of from 8 to 12 percent by weight.
11. A composition as recited in claim 10 wherein the organotin
polysiloxane is present in the range of from 12 to 16 percent by
weight.
12. A composition as recited in claim 9 wherein the organotin
polysiloxane is present in the range of from 12 to 16 percent by
weight.
13. A composition as recited in any of claims 2, 3, 4, 5, 6, 7, 8,
9, 10, 11 or 12, comprising a plasticizer for acrylic resin in the
range of from 0.5 to 5 percent by weight.
14. A composition as recited in any of claims 2, 3, 4, 5, 6, 7, 8,
9, 10, 11 or 12, comprising a slightly water soluble resin in the
range of from 1 to 10 percent by weight.
15. A composition as recited in any of claims 2, 3, 4, 5, 6, 7, 8,
9, 10, 11 or 12, wherein the solvent is present in the range of
from 24 to 36 percent by weight.
16. A composition as recited in any of claims 2, 3, 4, 5, 6, 7 or 8
wherein the balance of marine paint and toxicant agents is in the
range of from 30 to 45 percent by weight.
17. A composition as recited in claim 1 wherein m in the formula is
an average of at least about 5.
18. A composition as recited in claim 17 wherein R.sub.1, R.sub.2,
and R.sub.3 are each butyl.
19. A composition as recited in claim 1 wherein R.sub.1, R.sub.2,
and R.sub.3 are each butyl.
20. A composition as recited in claim 19 wherein R is selected from
the group consisting of hydrogen and ethyl radical.
21. A composition as recited in claim 20 wherein the X's are
selected so that the ratio of tin atoms to silicon atoms is in the
range of from 1.3:5 to 2.5:5.
22. A composition as recited in claim 21 wherein m in the formula
is an average of at least about 5.
23. A composition as recited in claim 1 wherein the weight ratio of
acrylic resin to organotin polysiloxane is in the range of from 0.5
to 1.0.
24. A composition as recited in claim 23 wherein the weight ratio
of acrylic resin to organotin polysiloxane is in the range of from
0.6 to 0.8.
25. A composition as recited in claim 1 comprising a copper bearing
antifouling agent selected from the group consisting of copper
powder and cuprous salts wherein the weight ratio of organotin
polysiloxane to the copper bearing antifouling agent is in the
range of from 0.5 to 1.5.
26. An antifouling coating composition comprising:
an acrylic resin binder;
an organotin polysiloxane having the formula: ##STR6## where m is
an average of up to about 10, each X is independently selected from
the group consisting of R and Y, where each R is selected from the
group consisting of hydrogen and ethyl radical, where each Y is a
tributyl tin radical and the X's are selected so that the ratio of
tin atoms to silicon atoms is in the range from 0.7:5 to 5:5;
copper bearing antifouling agent selected from the group consisting
of copper powder and cuprous salts;
a volatile organic solvent for the acrylic resin and organotin
polysiloxane; and
a sufficient balance of paint and toxicant agents selected from the
group consisting of pigment powders, fillers, thickening agents,
antisettling agents, zinc oxides, algicides, silica, clay, talc,
metal oxides, plasticizers and slightly water soluble resin for
forming a marine paint.
27. A composition as recited in claim 26 wherein the weight ratio
of the organotin polysiloxane to the copper bearing antifouling
agent is in the range of from 0.5 to 1.5.
28. A composition as recited in claim 27 wherein the copper bearing
antifouling agent is present in the range of from 10 to 30 percent
by weight of the composition.
29. A composition as recited in claim 27 wherein the weight ratio
of acrylic resin to organotin polysiloxane is in the range of from
0.5 to 1.0.
30. A composition as recited in claim 27 wherein the weight ratio
of acrylic resin to organotin polysiloxane is in the range of from
0.6 to 0.8.
31. A composition as recited in claim 26 wherein the weight ratio
of acrylic resin to organotin polysiloxane is in the range of from
0.5 to 1.0.
32. A composition as recited in claim 31 wherein the copper bearing
antifouling agent is in the range of from 10 to 30 percent by
weight of the composition.
33. A composition as recited in claim 32 wherein the organotin
polysiloxane is present in the range of from 7 to 25 percent by
weight of the composition.
34. A composition as recited in claim 33 wherein the acrylic resin
is present in the range of from 6 to 20 percent by weight of the
composition.
35. A composition as recited in claim 26 wherein the organotin
polysiloxane is present in the range of from 7 to 25% by weight of
the composition.
36. A composition as recited in claim 35 wherein the copper bearing
antifouling agent is present in the range of from 10 to 30 percent
by weight of the composition.
37. A marine antifouling paint comprising:
an acrylic resin binder;
an organotin polysiloxane having the formula ##STR7## where m is an
average of up to about 10, each X is selected independently from
the group consisting of R and Y, where each R is selected from the
group consisting of hydrogen and alkyl and alkoxyalkyl radicals
containing less than six carbon atoms, where each Y is a
trisubstituted tin radical having the formula ##STR8## where
R.sub.1, R.sub.2, and R.sub.3 are independently selected from the
group consisting of alkyl, cycloaklky and aryl radicals and
R.sub.1, R.sub.2, and R.sub.3 contain collectively up to about 18
carbon atoms and the X's are selected so that the ratio of tin
atoms to silicon atoms is in the range of from 0.7:5 to 5:5;
and
a copper bearing antifouling agent selected from the group
consisting of copper powder and cuprous salts.
38. A marine paint as recited in claim 37 wherein the organotin
polysiloxane is present in the range of from 7 to 25 percent by
weight of the paint.
39. A marine paint as recited in claim 38 wherein the copper
bearing antifouling agent is present in the range of from 10 to 30
percent by weight of the paint.
40. A marine paint as recited in claim 37 wherein the copper
bearing antifouling agent is present in the range of from 10 to 30
percent by weight of the paint.
41. A marine paint as recited in any of claims 37, 38, 39, or 40,
wherein the weight ratio of organotin polysiloxane to copper
bearing antifouling agent is in the range of from 0.5 to 1.5.
42. A marine paint as recited in any of claims 37, 38, 39, or 40
wherein the acrylic resin is present in the range of from 6 to 20
percent by weight of the paint.
43. A marine antifouling coating composition comprising:
polymethyl metharcrylate in the range of from about 8 to 12 percent
by weight;
an organotin polysiloxane having the formula ##STR9## where m is an
average of at least about 5, each X is independently selected from
the group consisting of R and Y, wherein each R is selected from
the group consisting of hydrogen and ethyl radical, where Y is a
tributyl tin radical and the X's are selected so that the ratio of
tin atoms to silicon atoms is in the range of from 1.3:5 to 2.5:5,
the organotin polysiloxane being present in the range of from 12 to
16 percent by weight;
a solvent for the acrylic resin and organotin polysiloxane in the
range of from 24 to 36 percent by weight;
a copper bearing antifouling agent selected from the group
consisting of copper powder and cuprous salts in the range of from
10 to 30 percent by weight;
a plasticizer compatible with the acrylic resin and organotin
polysiloxane in the range of from 0.5 to 5 percent by weight;
rosin in the range of from 1 to 10 percent by weight; and
a balance of primarily marine paint and toxicant agents selected
from the group consisting of pigment powders, fillers, thickening
agents, antisettling agents, zinc oxide, algicides, silica, clay,
talc, and metal oxides.
44. A marine antifouling coating composition comprising:
an acrylic resin in the range of from 6 to 20 percent by
weight;
a polysiloxane having substituted thereon trisubstituted organotin
moieties that are toxic to marine organisms, the proportion of
organotin moiety relative to the silicon content of the
polysiloxane being sufficient for the polysiloxane to be compatible
with the acrylic resin, the polysiloxane being in the range of from
7 to 25 percent by weight;
a solvent for the acrylic resin and the polysiloxane, in the range
of from 18 to 52 percent by weight; and
a balance in the range of from 10 to 65 percent by weight of
primarily marine paint and toxicant agents selected from the group
consisting of pigment powders, fillers, thickening agents,
antisettling agents, copper powder, cuprous salts, zinc oxide,
algicides, silica, clay, talc, metal oxides, plasticizers, and
slightly water soluble resins.
45. A composition as recited in claim 44 comprising a copper
bearing antifouling agent selected from the group consisting of
copper powder and cuprous salts in the range of from 10 to 30
percent by weight.
46. A composition as recited in claim 45 wherein the ratio of tin
atoms to silicon atoms is in the range of from 1.3:5 to 2.5:5.
47. A composition as recited in claim 44 wherein the ratio of tin
atoms to silicon atoms is in the range of from 1.3:5 to 2.5:5.
48. A composition as recited in claim 47 wherein the polysiloxane
is present in the range of from 12 to 16 percent by weight.
49. A composition as recited in claim 44 wherein the polysiloxane
is present in the range of from 12 to 16 percent by weight.
50. A composition as recited in any of claims 44, 45, 46, 47, 48 or
49 wherein the acrylic resin comprises polymethyl methacrylate in
the range of from 8 to 12 percent by weight.
51. A composition as recited in any of claims 44, 46, 47, 48, or 49
comprising a copper base antifouling agent selected from the group
consisting of copper powder and cuprous salts in the range of from
10 to 20 percent by weight.
Description
FIELD OF THE INVENTION
This invention relates to marine antifouling coating compositions
including an acrylic resin and a trisubstituted organotin
substituted polysiloxane in a paint mixture. Preferably, the
compositions also include copper or a copper salt for inhibiting
marine fouling.
BACKGROUND
When a ship moves through the water the drag resistance or water
frictional forces which must be overcome are responsible for as
much as half of the power consumed in operation of the vessel. The
surface condition of the hull is a major factor inducing drag. It
is therefore desirable to have an extremely smooth surface on the
hull and paint formulations have been developed that are very
smooth when cured and/or are polished by moving water to provide an
extremely smooth surface. It is desirable to have a coating
material that exhibits this polishing action to produce a
microsmooth surface to minimize the drag penalty due to
microroughness.
Fouling of the hull by pestiferous marine organisms is a major
source of drag. The use of antifouling protective coating on a
ship's hull is a primary approach to controlling fouling and the
resulting drag. The antifouling coating inhibits growth of marine
organisms on the hull to keep it smooth. Coatings can also be used
on static structures exposed to seawater to minimize growth of
organisms that could cause deterioration of such structures.
A truly effective antifouling coating meets at least three
criteria: (1) It will possess broad spectrum antifouling efficacy
(i.e., inhibit growth of a broad variety of organisms) for extended
periods of time, usually three years; (2) it will possess a smooth
surface so as not to cause a microroughness drag penalty; and (3)
it will actively reduce drag by reducing the roughness profile of
the surface.
To meet the first criterion it is necessary to deliver to the
surface of the coating in a controlled fashion, minimum effective
amounts of toxin or fouling control agents. The amount of toxin
delivered at the surface should not be substantially above the
minimum effective amount for inhibiting fouling to avoid premature
depletion of the antifouling agent.
One technique for controlling release of toxin involves the use of
latent toxicants which are activated by an environmental or
chemical trigger such as hydrolysis. This is the principal behind
the operation of organotin polysiloxane materials as described in
U.S. Pat. No. 4,080,190. In these materials a trisubstituted
organotin moiety is chemically bonded to a macromolecular
polysiloxane backbone. Through hydrolysis the organotin moiety is
gradually liberated and diffuses to the surface of the coating as
the active fouling control agent.
The organotin polysiloxane materials can act as binders, co-resins,
or toxic pigments or additives depending on the tin to silicon
ratio and related physical form. A low tin to silicon ratio permits
the organotin polysiloxane to perform as a binder. Such material is
primarily inorganic in nature though the presence of the organotin
groups do impart a certain degree of organic character. This
enhances compatability with organic materials and better adhesion
to metal substrates, for example, than a polysiloxane without
organotin substitution.
As a binder the organotin polysiloxane can serve as a matrix for
essentially inorganic fillers and pigments. The coating is
microporous allowing continual release of the toxic agent; that is,
an organotin radical is formed in situ through hydrolysis of the
tin-oxygen-silicon bond. Such continual release of toxicant avoids
surface passivation as frequently occurs in conventional copper
based antifouling coatings. Since this type of formulation is
microporous, performance is essentially independent of turbulence;
that is, sufficient toxicant is leached to the surface for
preventing fouling under either static or dynamic conditions.
With a higher tin to silicon ratio the organotin polysiloxane can
be an additive in a coating composition using a variety of binders.
In such a composition the release of toxicant is a function of the
properties of the binder plus hydrolysis characteristics of the
organotin polysiloxane.
BRIEF SUMMARY OF THE INVENTION
There is, therefore, provided in practice of this invention
according to presently preferred embodiments, a marine antifouling
coating composition comprising an acrylic resin in the range of
from about 6 to 20% by weight, a polysiloxane having substituted
thereon trisubsituted organotin moieties that are toxic to marine
organisms, the polysiloxane being in the range of from about 7 to
25% by weight, a solvent for the acrylic resin and polysiloxane in
the range of about 18 to 52% by weight with the balance of the
composition in the range of from about 10 to 65% by weight being
primarily conventional marine paint and toxicant agents for
augmenting action of the organotin polysiloxane. It is particularly
preferred that the composition also include copper or copper salts
that are effective for inhibiting growth of marine organisms and
facilitating the release of toxins by controlling the seawater
sensitivity of the film.
DESCRIPTION
The marine antifouling coating composition provided in practice of
this invention comprises a mixture of resins or binders, solvent
and pigments or fillers, along with associated marine paint and
antifouling ingredients in a consistency suitable as a paint for
brushing, spraying, or the like on ship hulls or other structures
exposed to seawater.
The binders in the composition comprise an acrylic resin in the
range of from about 6 to 20% by weight and an organotin substituted
polysiloxane in the range of from about 7 to 25% by weight. A
volatile organic solvent for the acrylic resin and polysiloxane is
preferably present in the range of from about 18 to 52% by weight.
The balance of the composition in the range of from about 10 to 65%
by weight comprises conventional plasticizers, a small amount of
water soluble resin, pigment powders, fillers, thickening agents,
antisettling agents, copper powder, copper salts, zinc oxide,
algicides, clay, talc, metal oxides and the like.
It is particularly desirable that the composition include copper
powder or cuprous salts that are effective for inhibiting growth of
marine organisms. The combination of organotin polysiloxane,
acrylic resin and copper supplying antifouling agent appears to
avoid passivation of the copper bearing antifouling agent which
often occurs in seawater. Preferably the copper or cuprous salt is
present in a proportion of up to about 30% by weight.
The acrylic resin is selected from the group consisting of methyl
methacrylate, ethyl methacrylate, propyl methacrylate, isobutyl
methacrylate, and n-butyl methacrylate. Such materials can be used
separately or as polymer blends. Preferably the acrylic resin is
polymethyl methacrylate since economical, readily commercially
available, and an excellent resin for marine coatings. The methyl
methacrylate forms a microsmooth coating and has appropriate
characteristics in moving seawater to maintain a low drag profile
on a vessel.
The acrylic resin is present in the composition in the range of
from about 6 to 20% by weight. If the acrylic resin is present in a
proportion less than about 6% by weight, adhesion of the coating to
metal substrates can be excessively degraded. Further, the
microsmoothness and ablation characteristics of the resultant
coating may not be adequate for minimizing drag when used on a ship
or the like. If the proportion of acrylic resin is more than about
20% by weight, the amount of polysiloxane in the composition may
need to be reduced to a level that the antifouling properties of
the coating are degraded.
Preferably the acrylic resin is present in the range of from about
8 to 12% by weight. Such proportions are found to give an excellent
balance of adhesion of the coating composition to a variety of
substrates, microsmoothness and ablation characteristics suitable
for reducing drag and long life as an antifouling coating. A
particularly preferred composition has from about 10 to 11 % by
weight of acrylic resin.
The organotin polysiloxane comprises a polymeric precursor having
the formula ##STR1## where m is in the range up to an average of
about 10 and preferably is an average of at least about 5. In this
formula each X is independently selected from the group consisting
of R and Y. Each R is selected from the group consisting of
hydrogen, and alkyl and alkoxyalkyl radicals containing less than
six carbon atoms. Each Y in the formula is a trisubstituted
organotin radical having the formula: ##STR2## In this organotin
moiety R.sub.1, R.sub.2 and R.sub.3 are independently selected from
the group consisting of alkyl, cycloalkyl, and aryl radicals and
collectively contain up to about 18 carbon atoms. Preferably
R.sub.1, R.sub.2 and R.sub.3 are each butykl for optimum toxicity
of the composition to marine organisms. Triphenyl tin polysiloxane
can be substituted for some of the tributyl tin siloxane in some
embodiments.
Preferably the R radical on the polysiloxane is ethyl. When the
siloxane is polymerized by hydrolysis and condensation, the
reaction by-product is ethyl alcohol which has a volatility similar
to the organic solvents in the composition, thereby making the
composition readily applicable as a paint. If desired, the
polysiloxane can be prehydrolyzed when making up the composition to
speed polycondensation in which case at least a portion of R is
hydrogen. Such prehydrolysis can reduce the shelf life of the
composition.
Such organotin polysiloxane and methods for making them are
described in U.S. Pat. No. 4,080,190, which is hereby incorporated
by reference.
In the polysiloxane m represents the average number of silicon
atoms per molecule. Generally there is a random distribution of
molecules having more or less than m silicon atoms. For example,
when m=5, molecules containing 4, 5 and 6 silicon atoms can be
present. Preferably, m is less than about 10 so that the siloxane
can be properly polymerized by hydrolysis and polycondensation
during curing of the coating composition. Preferably m is an
average of about 5. Such a polysiloxane can polymerize, following
transesterification to introduce the organotin moiety, to produce
linear and/or crosslinked polymers. Such material has a high silica
content, hence a relatively high proportion of solid binder
following polycondensation and removal of the preferred ethyl
radical.
The X's in the formula are selected so that the ratio of the tin
atoms to silicon atoms in the organotin polysiloxane is in the
range of from about 0.7:5 to 5:5.
If the ratio of tin atoms to silicon atoms in the composition is
less than about 0.7 tin atoms for every 5 silicon atoms, the
quantity of the trisubstituted tin moiety can be so low that
toxicity of the coating to marine organisms is marginal. When the
tin to silicon ratio is low, extensive cross-linking of the
polysiloxane can be obtained so that the polysiloxane forms a
durable binder in the coating composition. This permits a higher
proportion of polysiloxane and a lower proportion of acrylic resin
in the composition without degrading the desired mechanical
properties of the resultant coating.
The proportion of tin atoms to silicon atoms should be less than
about 5:5 for polymerization of the polysiloxane. The
trisubstituted tin moiety on the polysiloxane introduces sufficient
steric hindrance that at high tin to silicon ratios cross-linking
is inhibited. Thus, with high tin to silicon ratios, the mechanical
properties of the polymerized siloxane are reduced. In such an
embodiment the proportion of acrylic resin to polysiloxane is
increased for maintaining the mechanical properties of the coating.
At high tin to silicon ratios in the polysiloxane, conventional
plasticizers may be omitted as the polysiloxane blend with the
acrylic resin can provide sufficient plasticizing.
Preferably, the tin to silicon ratio in the polysiloxane is in the
range of from about 1.3:5 to 2.5:5. A particularly preferred
composition has a ratio of tin atoms to silicon atoms of about
2.5:5. A composition having a ratio of about 1.3 tin atoms for
every 5 silicon atoms in the polysiloxane forms an excellent binder
for the coating composition with sufficient trisubstituted
organotin moiety for high toxicity of marine organisms. Such a
composition can be useful where a durable antifouling coating is
desired with low polishing action. In such an embodiment a
relatively higher proportion of polysiloxane and relatively lower
proportion of acrylic resin may be used in the composition. A
particularly preferred composition has a ratio of about 2.5 tin
atoms per 5 silicon atoms. Such material is not completely
cross-linked and serves to modulate the properties of the acrylic
resin in the coating composition. A high proportion of tin moiety
is present in the composition providing long life antifouling
characteristics. Such a material has about the optimum balance of
mechanical properties and toxicity.
It will be recognized that the quantity of organotin polysiloxane
binder in the composition following hydrolysis and condensation
will be less than the proportion of organotin siloxane in the
uncured coating composition. For example, when the organotin
siloxane comprises a tributyl tin moiety on an ethoxy siloxane
wherein each molecule has an average of five silicon atoms and the
ratio of tin atoms to silicon atoms is about 2.5:5, the cured
siloxane has about 73% of the weight of the uncured precursor. The
weight loss comes about from loss of the ethyl radical upon
hydrolysis and condensation.
The acrylic resin and organotin polysiloxane in the composition act
as co-resins forming a binder for a paint coating. Evaporation of
the solvent from the composition and exposure of the composition to
environmental water or water vapor results in solidification of the
binder blend through deposition of the acrylic resin and concurrent
hydrolytic polycondensation of the siloxane. Depending on the
proportions of the materials, this binder system can be in the form
of a resin blend or an interpenetrating polymer network.
Preferably the organotin polysiloxane is present in the composition
in the range of from about 7 to 25% by weight. If the proportion is
less than about 7% by weight, the quantity of the organotin moiety
can become so low that the antifouling characteristics of the
composition can be too low for practical use. The rate of release
of toxicant at the coating surface can be less than the minimum
required for inhibiting growth of organisms.
If the proportion of organotin polysiloxane in the composition is
more than about 25% by weight, the mechanical properties of the
organotin polysiloxane can predominate over those of the acrylic
resin, thereby reducing the desirable properties of the acrylic.
Further, high proportions of organotin polysiloxane can reduce the
content of other toxicants such as copper bearing antifouling
agents, thereby narrowing the spectrum of organisms against which
the antifouling coating is effective.
Preferably the organotin polysiloxane is present in the composition
in the range of from about 12 to 16% by weight. This gives a good
balance of the antifouling properties of the siloxane and the
mechanical properties of the acrylic. Such a coating has a long
useful lifetime in both static and dynamic fouling control
situations.
Preferably the quantity of organotin polysiloxane is somewhat
larger than the proportion of acrylic resin in the composition.
Preferably the weight ratio of acrylic resin to organotin
polysiloxane is in the range of from about 0.5 to 1.0 and most
particularly in the range of from about 0.6 to 0.8. These provide
optimum balance of antifouling characteristics in the combination
of controlled release of toxicant and mechanical properties in the
resultant coating.
As co-resins in the binder system the organotin polysiloxane
moderates the physical properties of the acrylic resin. Ordinarily,
a polysiloxane is incompatible with an acrylic resin, however, it
is found that the presence of the trisubstituted organotin moiety
on the polysiloxane makes the two types of binder compatible so
that a coating composition with reasonable shelf life can be
formulated.
In the cured composition, the acrylic in the binder provides a
microsmooth surface that minimizes microroughness drag penalty, and
a slow controlled polishing action can be obtained for providing
maximum reduction of drag. In the preferred embodiment of this
invention, the surface profile roughness envelope is in the 15 to
25 micron range throughout the service life of the coating and its
ablation rate is less than 3 microns of coating loss per month at a
speed of 15 knots. The organotin moiety in the binder is released
at a controlled rate since it is chemically bonded to a polymeric
content of the coating and is not free to migrate or diffuse before
hydrolysis frees the tin moiety from the polysiloxane.
In other compositions in which an acrylic resin is used as binder
and antifouling agents are included as additives, such as cuprous
salts or tributyltin oxide, the toxicant is released at a rate
controlled only by matrix properties. Since diffusion rate depends
on concentration, release of toxicant at the surface is relatively
high when the coating is fresh and diminishes steadily thereafter.
To maintain an effective release rate at the surface after a long
time, an excessive release rate is needed in the beginning.
In a composition with organotin polysiloxane and acrylic resin,
release of toxicant occurs upon hydrolysis of the
tin-oxygen-silicon bond. The rate of release is thus controlled by
the rate of hydrolysis which remains steady throughout the life of
the coating. Since the rate of release is nearly constant, the
amount of toxicant can be selected to provide slightly more than an
effective amount at the projected end of the useful life of the
coating. Little excess toxicant is released during the early life
of the coating and longer life can be obtained for a selected total
amount of toxicant.
An organic solvent for the acrylic resin and organotin polysiloxane
is preferably present in the range of from about 18 to 52% by
weight. Xylene is an excellent solvent for both the acrylic resin
and polysiloxane. In an exemplary embodiment acrylic resin is
included in the composition by way of a commercially available
solution of acrylic resin and toluene. In such an embodiment the
solvent in the composition comprises a blend of toluene and xylene.
Other nonpolar solvents for acrylic resin and polysiloxane can also
be used, along with limited amounts of alcohols. Exemplary solvents
are xylene, toluene, various Cellosolves, naphtha and mineral
spirits. The organic solvents should be selected to provide a
volatility that permits drying of the coating composition in a
reasonable time when applied to the hull of a vessel or other
substrate.
The proportion of solvent in the composition is subject to rather
wide variation and is determined largely by the desired viscosity
in the composition to permit application to substrates by spraying,
brushing, or the like. If the proportion of solvent is less than
about 18% by weight, the viscosity of the composition may be so
high that application to substrates in coatings of reasonable
thickness is rather difficult. Levelling to obtain a smooth coating
may also be inhibited. If the composition has more than about 52%
by weight of solvent, application of coatings of reasonable
thickness can be limited by sagging or running. Preferably, the
solvent is present in the range of from about 24 to 36% by weight.
It is found that such a proportion of solvent with the preferred
resin compositions and other marine paint additives hereinafter
described provides a viscosity range quite suitable for application
to substrates by brushing and/or spraying.
A variety of other ingredients can form the balance of the
composition in the range of from about 10 to 65% by weight. Such
additional ingredients are conventional additions to marine paints
and are employed for modifying the properties of the coating
composition or providing antifouling toxicity.
In addition to the organotin substituted polysiloxane, other marine
antifouling ingredients can be included in the composition, in
particular it is found desirable to include up to about 30% by
weight of copper powder and/or cuprous salts, such as Cu.sub.2 O,
CuSCN, Cu.sub.2 S, CuOH, or the like in the composition. Cuprous
oxide is a preferred copper base antifouling agent. Such copper
based materials are widely recognized as agents for inhibiting
growth of marine organisms and are desirable additives in the
marine coating composition. Preferably such copper base antifouling
agents are present in the composition in the range of from about 10
to 20% by weight.
When the copper bearing antifouling agent is present at less than
about 10 weight percent, the minimum effective release rate may not
be achieved over a long lifetime of the coating. If the proportion
is much above about 20%, passivation of the copper agent may occur
under some conditions.
It is desirable to include copper bearing antifouling agents in the
composition for enlarging the spectrum of marine organisms combated
by the antifouling coating. Copper and cuprous salts tend to be
somewhat more effective for inhibiting growth of algae and more
primitive soft organisms, whereas the organotin moiety is somewhat
more effective against higher organisms, barnacles or the like,
which are often referred to as "hard" fouling. When the proportion
of copper base antifouling agent is on the order of about 15% by
weight, good long-life antifouling characteristics are obtained
without decreasing the other desirable properties of the
coating.
When a copper based antifouling agent is included in the
composition, it is also desirable to include zinc oxide in a
proportion of about one-half the proportion of copper base
antifouling agent. The zinc oxide is desirable since it potentiates
the antifouling activity of the copper by enhancing the transport
of copper ion across the biological membranes of marine organisms.
Zinc oxide can also promote galvanic release of copper from the
antifouling coating. An excess amount of zinc oxide can suppress
the antifouling activity of the copper, hence, it is desirable that
the maximum zinc oxide be in a proportion of about 50% of the
copper base antifoulant. If zinc is included in the composition,
the proportion of zinc oxide should be reduced.
It is believed that no single toxicant is available for
compositions that can be applied to surfaces in practical
situations and that will universally protect marine surfaces
against fouling. While organotin compounds are very effective as
antifouling toxicants, practical compositions that provide
controlled release of toxicant over long periods of time do not
have sufficiently broad antifouling properties for the full
spectrum of organisms. It is found, however, that by combining the
organotin polysiloxane with other toxicants, such as copper or
cuprous salts or organic algicides, the antifouling performance of
the coating can be effective in a wide variety of fouling
environments for periods of time far in excess of conventional
coatings. This effectiveness is present under both static and
turbulent conditions. This differs from prior compositions for
controlled release of toxicants which are optimized for either
static or dynamic conditions, rather than both.
It is particularly advantageous to employ copper bearing
antifouling agents such as copper powder or cuprous salts as an
additional toxicant in a coating composition having trisubstituted
organotin polysiloxane and acrylic resin as binders. Ordinarily in
a seawater environment at least a portion of the copper is
converted to inactive salts, such as copper oxychlorides, which are
relatively ineffective in inhibiting growth of marine fouling
organisms. The reason that the acrylic and organotin polysiloxane
binders tend to stabilize the copper or copper salts in seawater is
not yet understood. It is believed that with organotin polysiloxane
in the composition, the amount of copper bearing antifouling agent
can be reduced, as compared with prior compositions, without
reducing antifouling activity. Lower copper concentration may avoid
passivation.
Preferably the weight ratio of trisubstituted organotin
polysiloxane to copper powder or cuprous salt in the composition is
in the range of from about 0.5 to 1.5. When the ratio is either
above or below this range there is a decrease in the spectrum of
organisms combated by the antifouling composition. A proportion
near the middle of this range appears to give the best broad
spectrum antifouling activity. It is also desirable that the weight
ratio of binders to copper powder or cuprous salt be in the range
of from about 0.8 to 2 to provide an appropriate range of strength
and controlled release of toxicant for good long life antifouling
activity. When the ratio of binder to copper bearing antifouling
agent is less than about 0.8 the erosin resistance of the coating
and the life of the copper constituent can be significantly
reduced. If the proportion of binder relative to the copper bearing
constituent is more than about 2, there is a reduction in the
availability of copper at the surface and a decrease in the
antifouling activity, particularly for algae and soft organisms
against which copper is particularly effective.
Preferably, the composition includes a conventional plasticizer for
the binders in the range of from about 0.5 to 5% by weight, and
most preferably about 0.5 to 2% by weight. The plasticizer imparts
flexibility and resilience to the cured composition. External
plasticizers that maintain their molecular identity are preferred,
rather than plasticizers that chemically bond in the polymer
system. A variety of conventional plasticizers that are compatible
with the acrylic resin and organotin polysiloxane are suitable,
such as alkyl benzyl, phthalates, dialkyl phthalates, phosphate
esters, sulfonamides, butyl phthalyl butyl glycolate, diphenyl
phthalate, dicyclohexyl phthalate, tricresyl phosphate, and the
like. The amount of plasticizer employed in the composition is
somewhat proportioned to the tin to silicon ratio in the
polysiloxane. A smaller amount of plasticizer can be used when the
tin to silicon ratio is high since the polysiloxane can also act as
a plasticizer. Conversely, when the tin to silicon ratio is low so
that the polysiloxane is extensively cross-linked and rigid, a
somewhat higher proportion of other plasticizer can be included in
the composition.
It is desirable to include a slightly water soluble resin in the
composition for enhancing gradual dissolution and ablation of the
coating. Addition of such resins that are slightly soluble in
seawater enhances the microporosity of the coating and can help
control the hydrolysis of the organotin moiety for maintaining
antifouling characteristics over a long lifetime. Preferably, the
water soluble resin is water white rosin, since it is economical,
easily blended into the composition, and quite suitable in
stability and water solubility. Other slightly soluble resins can
be substituted such as hydroxy ethyl methacrylate, polyvinyl
acetate, polyvinyl alcohol, or the like.
The proportion of water soluble resin in the composition depends on
the degree of solubility of the resin and desired rate of ablation
and penetration of water into the coating. For example, when rosin
is the seawater soluble portion of the composition, it is
preferably present in the range of from about 1 to 10% by weight,
and most preferably in the range of from about 3 to 6% by weight.
If the rosin is present at less than about 1% by weight, the
coating may become passivated, and antifouling characteristics
degraded, particularly when copper or copper salts are included in
the composition. Rosin content of more than about 10% by weight
leads to excessive ablation and short lifetime of such a coating.
Preferably, rosin is present in the range of from about 3 to 6% by
weight, to provide a good balance of coating lifetime and water
penetration to provide long antifouling activity.
It is highly desirable to include a thixotropic agent such as
alcohol swellable clay, talc, or colloidal silica. Such
conventional thickeners are widely used in paint compositions for
modifying viscosity and obtaining paints that can be sprayed or
brushed to provide a coating of reasonable thickness without
sagging or running. An exemplary thickening agent particularly
useful is dimethyl dioctodecyl ammonium bentonite available from
the Baroid Division of National Lead Company, Houston, Texas, as
Bentone 34. Preferably the thickener is present in the composition
in the range of from about 0.5 to 4% by weight and most preferably
in the range of from about 0.5 to 2.0% by weight, as is
conventional in paint compositions.
It is desirable to include antisettling agents for the copper base
materials and other fillers and pigments employed in the
composition. A variety of antisettling agents used in paint
compositions are suitable for preventing settling and minimizing
mixing that might be needed before a composition is used after a
prolonged shelf life. Antisettling agents are employed in marine
paint compositions up to about 3% by weight.
If desired, organic algicides can be included in the composition,
such as dichlorisothiazalone or diiodomethyl p-tolyl sulfone.
Preferably, such algicides are present in a proportion up to about
16% by weight, and most preferably up to about 5% by weight. Such
algicides can promote gelling of the composition and the
proportions are preferably kept low enough to inhibit such gelling
and maintain a long shelf life.
A variety of conventional fillers and pigments can also be included
in the coating composition. Such materials can modify the
properties of the paint as it is applied, such as body to promote
good spreading and leveling without runs or sags. Such materials
can also modify properties of the cured coating such as strength,
toughness, opacity and color. Pigments and fillers can also help
protect the substrate on which the coating composition is placed.
Exemplary pigments and fillers include red iron oxide, talc,
silica, titanium dioxide, chromium oxide, and the like.
Such pigments and fillers can be included in the composition up to
about 20% by weight. If present in a proportion more than about 20%
by weight, it becomes necessary to reduce the proportions of
algicides and other ingredients in the composition that are active
in inhibiting growth of marine organisms. Preferably the pigments
and fillers are present in the order of about 7% by weight which
provides good protection for substrates, opacity and strength.
The proportions of liquid and solid ingredients are selected so
that the composition can be sprayed or brushed onto a variety of
substrates as a marine paint.
Miscellaneous other ingredients can also be included in the
composition. Zinc powder can be included for inhibiting corrosion.
A small amount of phosphoric acid (e.g., 0.5%) can be included for
inhibiting premature gelling. The composition is preferably
packaged in a single container for ready use as a paint. If desired
it can be prepared in two packages for longer shelf life and mixed
shortly before use. Many other modifications and variations will be
apparent.
When the coating composition is applied to a surface, concurrent
effects are occurring in the acrylic and polysiloxane binders. The
acrylic resin forms a solid binder network as the volatile solvents
evaporate. The organotin polysiloxane hydrolyzes and condenses. If
desired, the polysiloxane can be at least partially hydrolyzed
before application of the coating. Such prehydrolysis can be
desirable for rapid cure of the coating but the shelf life of the
mixture may be decreased. Hydrolysis of the polysiloxane can occur
from ambient water vapor of exposure to water. A variety of bases
or acids can be present in small quantities to promote hydrolysis
as described in U.S. Pat. No. 4,080,190. Algicides, zinc oxide and
other ingredients in the composition can be sufficient to promote
hydrolysis. It might be noted that use of some basic promoters of
hydrolysis may not be totally compatible with copper bearing
antifouling agents. Such promoters may be omitted or the
composition used within a reasonable time after mixing, or the
copper bearing materials can be added shortly before applying the
coating.
EXAMPLES
Table I sets forth the compositions of six antifouling coating
compositions prepared in practice of this invention. The
compositions were mixed much as one would mix other paint
compositions. The compositions were applied to standard test panels
by spraying and the test panels were immersed in seawater at
Daytona Beach, Florida, for determining antifouling activity.
TABLE I ______________________________________ EXAMPLES INGREDIENT
A B C D E F ______________________________________ Acryloid B-48N
26.8 26.8 17.8 18.0 26.8 22.5 OTPS 15.3 15.2 12.2 12.4 15.2 14.7
Cuprous oxide -- 22.2 19.0 18.7 17.0 15.5 Zinc oxide 8.0 8.8 8.8
8.9 9.0 7.5 Ethyl aminoethanol 0.8 0.8 -- -- 1.1 0.8
Di-isodecylphthalate 1.0 2.0 1.3 1.2 2.0 1.2 W. W. Rosin 4.2 4.8
5.8 5.9 4.8 4.0 Red iron oxide 11.4 -- 2.8 7.4 -- 2.4 Nytal 300 7.0
2.5 2.5 -- 3.0 2.1 MPA-1078X -- -- 1.9 -- -- 1.6 Bentone 34 1.5 1.3
0.9 0.9 0.7 1.1 Neosol 0.4 0.4 0.3 0.2 0.2 0.3 Amical 48 -- -- 6.0
-- -- -- C-9211 6.0 6.0 -- 6.1 6.0 6.6 Xylene 17.6 9.2 20.7 18.5
14.2 19.7 TOTAL 100.0 100.0 100.0 100.0 100.0 100.0
______________________________________
The proportions of ingredients listed in Table I are set forth in
percentages by weight for each of the six coating compositions. The
materials set forth in Table I are identified as follows:
Acryloid B-48N comprises a solution of methyl methacrylate in
toluene available from Rohm and Haas, Philadelphia, Pennsylvania.
The solution has 45% by weight polymethyl methacrylate and 55% by
weight toluene.
OTPS refers to organotin polysiloxane. In each of the coating
compositions set forth in Table I, the organotin polysiloxane had
the formula: ##STR3## where m was an average of about 5 and X was
either an ethyl radical or a tributyl tin radical and the X's were
selected so that the ratio of tin atoms to silicon atoms was about
2.5:5.
Cuprous oxide is present as a finely divided powder which, as
pointed out above, inhibits growth of marine organisms. Zinc oxide
is also present as a finely divided powder and serves as a pigment
plus potentiating the activity of the copper salt.
Ethyl aminoethanol is present in the composition to promote
hydrolysis and condensation of the siloxane. Di-isodecylphthalate
is present as an external plasticizer for the acrylic and siloxane
binders. W. W. rosin (water white rosin) is present as a slightly
water soluble resin to modify the binder matrix and help control
gradual release of toxicants when the coating is immersed in
seawater.
Red iron oxide is present in the form of a powder serving as a
pigment. The pigment improves the strength and opacity of the
composition. Nytal 300 is a finely divided talc available from R.
T. Vanderbilt Company, Norwalk, Connecticut. The talc is present as
a filler that improves viscosity of the coating composition and
inhibits sagging.
MPA-1078X available from Baker Castor Oil Company, Bayonne, New
Jersey, is a colloidal thixotropic agent used to prevent settling
of solid powders. It is added as a paste of solids dispersed in a
solvent of xylene or toluene.
Bentone 34, available from National Lead Company, Baroid Division,
Houston, Texas, is finely divided dimethyl dioctodecyl ammonium
bentonite for thickening the composition and aiding in suspension
of solids.
Neosol, available from Shell Chemical Company, Houston, Texas, is
ethyl alcohol denatured with small amounts of methyl isobutyl
ketone, ethyl acetate and aviation gasoline. As a preliminary step
in formulating the coating composition the Neosol is mixed with the
Bentone 34 to form a paste and cause swelling of the Bentone
34.
Amical-48 available from Abbott Laboratories, North Chicago,
Illinois, comprises di-iodomethyl p-tolyl sulfone and serves as an
additional algicide.
C-9211 is a 4,5-dichloro-2-n-octyl-4-isothiazalin-3-one algicide
available from Rohm and Haas Company, Philadelphia, Pennsylvania.
The algicide can also provide a source of protons to promote
hydrolysis of the siloxane. It is desirable in preparing a
composition to add the algicide after all of the other ingredients
have been mixed to minimize the possibility of premature
gelation.
The composition is made by first diluting the acrylic resin
solution with additional solvent. Some of the xylene can be
reserved for making a paste of the solid ingredients to speed
mixing. The organotin polysiloxane is added and mixed, followed by
the plasticizer. After all of the liquid and soluble materials have
been mixed, the solid materials are added with as much mixing shear
as required to obtain a smooth paint composition. The order of
adding ingredients to the composition is not critical, although it
is desirable to add the algicide or any catalyzing amine last in
order to minimize premature gelation.
The coating compositions set forth in Table I were applied to
standard blank panels of primer coated steel or plastic for
measuring resistance to marine fouling. These panels were then
exposed to sewater at Daytona Beach, Florida. The fouling
resistance of the composition as a function of months of exposure
is set forth in Table II.
TABLE II ______________________________________ HARD FOULING ALGAL
FOULING EXAMPLE 6 12 18 24 Mos. 6 12 18 24 Mos.
______________________________________ A 10 10 10 10 9 5 5 0 B 10
10 10 10 10 9 9 9 C 10 10 9 -- 10 10 10 -- D 10 10 9 -- 10 10 10 --
E 10 10 10 -- 10 10 10 -- F 10 10 10 -- 10 10 10 -- Control 0 0 0 0
0 0 0 0 ______________________________________
Control panel refers to a blank panel with no antifouling coating.
Hard fouling refers to the growth of barnacles and similar
organisms with hard body parts. Algal fouling refers to algae and
other soft organisms. The ratings of the test panels for fouling
resistance is on a scale of 0 to 10, where 10 represents no fouling
whatsoever, 9 represents a very minor or trace amount of fouling, 5
represents approximately 50% of the test panel fouled and 0
represents complete failure or fouling over the entire surface.
* * * * *